1. Statement of the Technical Field
The inventive arrangements relate generally to methods and apparatus for providing increased design flexibility for RF circuits and, more particularly, to resonant cavities using conductive fluids.
2. Description of the Related Art
Resonant cavities are well known radio frequency (RF) devices and are commonly used in a variety of RF circuits, for example, in conjunction with microwave antennas and local oscillators. Resonant cavities are typically completely enclosed by conducting walls that can contain oscillating electromagnetic fields. An aperture is generally provided in one of the resonant cavity walls through which RF energy can be transmitted into, and extracted from, the resonant cavity. Resonant cavities can be constructed with a variety of shapes and can be used for different applications and frequency ranges. Nonetheless, the basic principles of operation are the same for all resonant cavities.
A resonant cavity resonates at frequencies which are determined by the dimensions of the resonant cavity. As the cavity dimensions increase, the resonant frequencies tend to decrease, and vice versa. For example, the lowest resonant frequency of a three dimensional rectangular resonant cavity is given by the equation:   f  =                    C        0            ⁢                                    1                          a              2                                +                      1                          b              2                                                  2      ⁢                                    μ            r                    ⁢                      ɛ            r                              where a and b the two largest dimensions of the cavity (i.e. length and width), ∈r is the relative permittivity of the dielectric within the resonant cavity, μr is the relative permeability of the resonant cavity, and C0 is the speed of light.
Resonant cavities provide many advantages for RF circuits operating in the microwave frequency range. In particular, resonant cavities have a very high quality factor (Q). In fact, cavities with a Q value in excess of 30,000 are not uncommon. The high Q gives resonant cavities an extremely narrow bandpass, which enables very precise operation of microwave devices utilizing the resonant cavities. In consequence to the narrow bandpass, however, resonant cavities are typically limited to operating only at very specific frequencies.
To alter the resonant frequency of a resonant cavity would typically require a mechanical manipulation of the shape and structure of the dimensions of the cavity. With rigid conventional dielectric or conductive materials, such manipulations would likely be costly and limited to certain specific structures and frequencies. Thus, a need exists for tuning a resonant cavity in a flexible and cost effective manner.